Forbid callable references to members and extensions with empty LHS

This syntax is reserved to be likely used in the future as a shorthand for
"this::foo" where the resulting expression doesn't take the receiver as a
parameter but has "this" already bound to it

js/js.translator/testData/expression/invoke/cases/invokeWithImplicitDispatchReceiverAndExtensionReceiver.kt

@@ -3,10 +3,10 @@ package foo
 fun A.f(s: String) = value + s
 
 class A(val value: String) {
-    fun bar(s: String) = (::f)(this, s)
+    fun bar(s: String) = (A::f)(this, s)
 }
 
-fun A.baz(s: String) = (::f)(this, s)
+fun A.baz(s: String) = (A::f)(this, s)
 
 fun box(): String {
     val a = A("aaa")